1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine such as an outboard motor and the like, and particularly to an ignition apparatus which improves the startability of the internal combustion engine.
2. Description of Related Art
FIG. 1 shows a circuit diagram of a conventional ignition apparatus of the capacitor discharge type for an internal combustion engine. In the figure, reference numeral 1 designates a power coil of a magneto generator (not shown) driven by an engine (not shown). The power coil 1 generates an alternating current output in synchronism with the rotation of the engine. The power coil 1 is connected to the anode of a diode 2 which rectifies the alternating current output from the power coil 1, and a cathode of the diode 2 is connected to a capacitor 3 which is charged by the output of the diode 2. Reference numeral 4 designates a signal coil which generates an ignition signal corresponding to the ignition timing of the engine. The signal coil 4 is installed on the magneto generator and generates an alternating current output in synchronism with the rotation of the engine. The signal coil 4 is connected to the anode of a diode 6 which rectifies the alternating current from the signal coil 4 through a resistance 5 which limits the alternating current of the signal coil 4. The cathode of the diode 6 is connected to the gate of a thyristor 7 which is rendered by receiving the ignition signal of the signal coil 4 and discharges the electric charge of the capacitor 3 through an ignition coil 8. In addition, reference numeral 9 designates a spark plug which emits sparks by receiving high voltage generated at the ignition coil 8.
Next, an explanation will be given. Alternating current from the power coil 1 is rectified by the diode 2, and the capacitor 3 is charged. The ignition signal generated by the signal coil 4 corresponding to the ignition timing of the engine is applied to the gate of the thyristor 7 through the resistance 5 and the diode 6. When the ignition signal is applied and the thyristor 7 is, gated on the electric charge stored in the capacitor 3 is discharged through the primary coil of the ignition coil 8. When the electric charge is discharged, a high voltage is generated at the secondary coil of the ignition coil 8 and fires the spark plug 9.
In an ignition apparatus having the above-described construction, there are problems in that the startability of engine at a low temperature is poor, and the rotation of the engine is unstable, even after starting, until the engine temperature rises. In order to solve these problems, the ignition timing is advanced for a predetermined period after starting, however, as it always has a constant spark advance characteristic both at the lower temperature period and at the high temperature period of the engine, the ignition timing is advanced even at the high temperature period of the engine at which time there is no need to advance, resulting in the rotation of engine being unnecessarily high. In order to solve the problem, it is possible to install a temperature sensor, however, the construction in that case is complicated resulting in an apparatus of high cost.